Laser system chiller

ABSTRACT

A laser system includes a laser element, a pump source configured to input light to the laser element, a first cooling circuit and a second cooling circuit. The first cooling circuit includes a first pump configured to drive a first flow of cooling liquid through a first fluid pathway, a first primary heat exchanger configured to cool the first flow of cooling liquid, and a laser element heat exchanger configured to remove heat from the laser element using the first flow of cooling liquid. The second cooling circuit includes a second pump configured to drive a flow of cooling liquid through a second fluid pathway, a second primary heat exchanger configured to cool the second flow of cooling liquid, and a pump source heat exchanger configured to remove heat from the pump source using the first and second flows of cooling liquid.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of U.S.provisional patent application Serial No. 61/614,124, filed Mar. 22,2012, the content of which is hereby incorporated by reference in itsentirety.

BACKGROUND

Embodiments of the present invention generally relate to laser systemsand, more specifically, to a chiller for use in a laser system.

High power laser systems have a broad range of applications throughoutthe scientific, industrial and medical fields. Laser systems generallyinclude a pump source, a laser element and a laser resonator. The pumpsource may include laser diodes or bars that generate pump energy or alight input to the laser element. The laser element absorbs the pumpenergy and emits laser light responsive to the absorbed energy. Thelaser resonator operates to generate a harmonic of the laser light.

The laser element is generally tuned to absorb pump energy having awavelength that is within a specified operating band. The wavelength ofthe pump energy varies with a temperature of the laser diodes and thecurrent supplied to the laser diodes. As a result, it is important tomaintain the pump source within an operating temperature range to ensurethat the pump energy is within the operating band of the laser element.

Laser systems utilize a chiller that operates to cool the pump sourceand the laser element. The chiller generally circulates cooled liquidthrough heat exchangers coupled to the pump source and the laserelement. The liquid absorbs heat from the heat exchangers to cool thepump source and the laser element. Conventional chillers generallymaintain the pump source and the laser elements at the same temperature.

SUMMARY

Embodiments of the invention are directed to a laser system comprising achiller configured to maintain a laser element and a pump source withincorresponding operating temperature ranges. In some embodiments, thelaser system includes a laser element, a pump source configured to inputlight to the laser element, a first cooling circuit and a second coolingcircuit. The first cooling circuit includes a first pump, a firstprimary heat exchanger and a laser element heat exchanger. The firstpump is configured to drive a first flow of cooling liquid through afirst fluid pathway. The first primary heat exchanger is configured tocool the first flow of cooling liquid. The laser element heat exchangeris configured to remove heat from the laser element using the first flowof cooling liquid. The second cooling circuit includes a second pump, asecond primary heat exchanger and a pump source heat exchanger. Thesecond pump is configured to drive a flow of cooling liquid through asecond fluid pathway. The second primary heat exchanger is configured tocool the second flow of cooling liquid. The pump source heat exchangeris configured to remove heat from the pump source using the first andsecond flows of cooling liquid.

In accordance with other embodiments, the laser system includes a laserelement, a pump source configured to input light to the laser element, afirst heat exchanger, a pump source heat exchanger, a laser element heatexchanger and a pump. The first heat exchanger is configured to cool afirst flow of cooling liquid. The pump source heat exchanger isconfigured to remove heat from the pump source using the first flow ofcooling liquid. The laser element heat exchanger is configured to removeheat from the laser element using a second flow of cooling liquid. Thepump is configured to drive the first and second flows of coolingliquid.

In accordance with other embodiments, the laser system includes a laserelement, a pump source configured to input light to the laser element, afirst cooling circuit and a second cooling circuit. The first coolingcircuit includes a first pump, a laser element heat exchanger and afirst reservoir. The first pump is configured to drive a first flow ofcooling liquid through the first fluid pathway. The laser element heatexchanger is in the first fluid pathway and is configured to remove heatfrom the laser element using the first flow of cooling liquid. The firstflow of cooling liquid is discharged from the first reservoir. Thesecond cooling circuit includes a second pump, a primary heat exchanger,a pump source heat exchanger and a second reservoir. The second pump isconfigured to drive a second flow of cooling liquid. The primary heatexchanger is configured to cool the second flow of cooling liquid. Thepump source heat exchanger is configured to remove heat from the pumpsource using at least a portion of the second flow of cooling liquid.The second reservoir is configured to receive the portion of the secondflow of cooling liquid fed to the pump heat exchanger. The firstreservoir is configured to receive a portion of the second flow ofcooling liquid output from the primary heat exchanger.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. The claimed subject matter is not limited to implementationsthat solve any or all disadvantages noted in the Background.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of an exemplary surgical laser system inaccordance with embodiments of the invention.

FIGS. 2-4 are schematic diagrams of a chiller formed in accordance withembodiments of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the invention are described more fully hereinafter withreference to the accompanying drawings. The various embodiments of theinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. Elements that are identified using the same orsimilar reference characters refer to the same or similar elements.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. Thus, a first element could be termed a secondelement without departing from the teachings of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 is a simplified diagram of an exemplary laser system 100 inaccordance with embodiments of the invention. While the depicted lasersystem 100 is a surgical laser system, it is understood that embodimentsdescribed herein are applicable to other types of laser systems as well.In general, the laser system 100 is configured to generateelectromagnetic radiation 102 in the form of a laser beam, deliver theelectromagnetic radiation through a laser fiber 104, such as a waveguideor optical fiber, to a probe tip 106 where it is discharged to a desiredtarget, such as tissue of a patient.

The exemplary system 100 comprises a laser resonator 108. The laserresonator 108 may include a first resonator mirror 110, a secondresonator mirror 112 and a laser element or rod 114. In one embodiment,the laser element 114 comprises a yttrium-aluminum-garnet crystal rodwith neodymium atoms dispersed in the YAG rod to form a Nd:YAG laserelement. Other conventional laser elements 114 may also be used.

The laser element 114 is pumped by a light input 116 from a pump source118, such as a diode stack or other pump source, to produce laser lightor beam 120 at a first frequency. The laser resonator 108 also includesa nonlinear crystal 122, such as a lithium borate (LBO) crystal or apotassium titanyl phosphate crystal (KTP), for generating a secondharmonic of the laser beam 120 emitted by the laser element 114. Thelaser beam 120 inside the resonator 108 bounces back and forth betweenthe first and second resonator minors 110 and 112, reflects off afolding minor 124, and propagates through the laser element 114 andnonlinear crystal 122. The laser element 114 has optical gain at acertain wavelength and this determines the wavelength of the laser beam120 inside the resonator 108. This wavelength is also referred to as thefundamental wavelength. For the Nd:YAG laser element 114, thefundamental wavelength is 1064 nm.

In one embodiment, the system 100 includes Q-switch 126 that convertsthe laser beam 120 to a train of short pulses with high peak power.These short pulses increase the conversion efficiency of the secondharmonic laser beam 102, and increase the average power of the laserbeam 102 outside the resonator 108.

When the laser beam 120 inside the resonator 108 propagates through thenonlinear crystal 122 in a direction away from the folding mirror 124and toward the second resonator minor 112, a beam 102 of electromagneticradiation at the second harmonic wavelength is output from the crystal122. The second resonator mirror 112 is highly reflective at both thefundamental and second harmonic wavelengths, and both beams 120 and 102propagate back through the nonlinear crystal 122. On this second pass,more beams 102 at the second harmonic wavelength are produced. Forexample, the nonlinear crystal 122 can produce a laser beam 102 having awavelength of approximately 532 nm (green) when a Nd:YAG rod is used asthe laser element 114. One advantage of the 532 nm wavelength is that itis strongly absorbed by hemoglobin in blood and, therefore, is usefulfor cutting, vaporizing and coagulating vascular tissue.

The folding mirror 124 is highly reflective at the fundamentalwavelength and is highly transmissive at the second harmonic wavelength.Thus, the laser beam 102 at the second harmonic passes through thefolding mirror 124 and produces a second harmonic laser beam 102 outsidethe optical resonator 108. The laser fiber 104 connects to an opticalcoupler 128, which couples the beam 102 to the optical fiber 104 througha shutter mechanism (not shown). The beam 102 travels through the laserfiber 104 to the probe 106, which is coupled to a distal end 130 of thelaser fiber 104. Embodiments of the probe 106 include components thatsupport the distal end 130 of the laser fiber, such as an endoscope orcystoscope.

The probe 106 generally includes a probe tip 132 where the laser beam102 is discharged. The probe tip 132 may include a fiber cap that isattached to the distal end of the optical fiber 104. The laser energymay be directed laterally from the probe tip by reflecting the laserenergy off a polished beveled surface at the distal end of the laserfiber 104. The fiber cap generally seals a cavity containing a gas (orvacuum) that maintains the necessary refractive index difference fortotal internal reflection at the beveled surface.

The laser system 100 may be controlled by a surgeon through a suitableinterface. The controls include a controller for selectively opening theshutter of the system 100 to allow for continuous or pulsed discharge ofthe laser beam 102 through the probe 106.

One embodiment of the laser system 100 includes a chiller 140,illustrated schematically in FIG. 1, formed in accordance withembodiments of the invention. The laser chiller 140 is configured tocontrol the temperatures of the laser element 114 and the pump source118. Conventional chillers maintain the laser element 114 at the sametemperature as the pump source 118, even though they have differentcooling requirements. This results in excess cooling power being appliedto the laser element 114, lower laser conversion efficiency while thelaser element 114 or the pump source 118 are not working at theiroptimal operating temperatures to match the pump spectra and laserelement absorption peaks, or the laser element 114 works at too highcooling temperatures. Unlike such conventional chillers, embodiments ofthe chiller 140, can maintain the laser element 114 and the pump source118 at different temperatures. This allows the laser resonator 108 tomaintain the laser element 114 and the pump source 118 within theiroptimal operating temperature ranges, while reducing energy consumptionand maximizing laser conversion efficiency. In some embodiments, thechiller 140 is configured to maintain the laser element 114 at atemperature of approximately 19° C., and maintain the pump source 118within an operating temperature range of 21-34° C. This typicallyrequires approximately 300 watts of cooling power to the laser elementheat exchanger 142 and approximately 725 watts to the pump source heatexchanger 144.

The chiller 140 generally comprises a laser element heat exchanger 142configured to cool the laser element 114 and a pump source heatexchanger 144 configured to cool the pump source 118. The heatexchangers utilized in the chiller 140 may be conventional heatexchangers used to exchange heat with a flow of cooling liquid, such asdeionized water. In some embodiments, the chiller 140 is configured tocool the Q-switch 126 using the pump source heat exchanger 142, oranother heat exchanger that shares a flow of cooling liquid with thepump source heat exchanger 142. Accordingly, while embodiments of thechiller 140 may only be described as operating to cool the laser element114, variations of these embodiments include the cooling of both theQ-switch 126 and laser element 114.

In one embodiment, the chiller 140 includes a controller 146representing one or more processors and memory containing instructionsexecutable by the one or more processors. The controller 141 isconfigured to perform method steps and control functions describedherein, such as processing signals from sensors and controlling pumpsand valves.

Additional embodiments of the chiller 140 will be discussed withreference to the schematic diagrams provided in FIGS. 2-4. Some details,such as refrigeration components, temperature and flow sensors, waterdeionizing circuits, filters, and other components are not illustratedin order to simplify the drawings.

FIG. 2 is a schematic diagram of a chiller 140A in accordance withembodiments of the invention. In some embodiments, the chiller 140Acomprises a cooling circuit 152 that operates to cool the laser element114 and a cooling circuit 154 that operates to cool the pump source 118.The cooling circuit 152 generally operates to maintain the laser element114 at a lower temperature than the temperature of pump source 118maintained by the cooling circuit 154. This allows the laser resonator108 to operate at a higher efficiency than conventional laser resonatorsthat maintain the Q-switch, the laser element, and the pump source atgenerally the same temperature, or provide the same amount of coolingpower to the components.

The cooling circuit 154 is generally configured to provide a flow ofcooling liquid 156 to the pump source heat exchanger 144 to maintain thepump source 118 within a desired operating temperature range, such as21-34° C. As mentioned above, this may require approximately 725 wattsof cooling power to the pump source heat exchanger 144, or to the flowof cooling liquid 156. The cooling circuit 152 generally operates toprovide a flow of cooling liquid 158 to the laser element heat exchanger142 to maintain the laser element 114, and optionally the Q-switch 126,within a desired operating temperature range. In one embodiment, thecooling circuit 152 is configured to maintain the laser element 114 atapproximately 19° C. As mentioned above, this typically requiresapproximately 300 watts of cooling power to the laser element heatexchanger 142.

In accordance with some embodiments of the chiller 140A, the coolingcircuit 154 includes a primary heat exchanger 160, a pump 162, and areservoir 164. The pump 162 drives the flow of cooling liquid 156 fromthe reservoir 164 along a fluid pathway 166, which travels through theprimary heat exchanger 160 and the pump source heat exchanger 144. Theheat exchanger 160 receives a flow of cooling refrigerant through acooling line 168, which is used to cool the flow of cooling liquid 156,in accordance with conventional heat exchangers. The passage of the flowof cooling liquid 156 through the pump source heat exchanger 144 coolsthe pump source 118 to maintain it within the desired operatingtemperature range. The flow of cooling liquid 156 discharged from thepump source heat exchanger 144 is delivered to the reservoir 164.

In some embodiments, the heat exchanger 160 cannot, by itself, fulfillthe cooling needs of the heat exchanger 144. That is, the heat exchanger160 is configured to provide fewer watts of cooling power than isrequired by the pump source heat exchanger 144 to maintain the pumpsource 118 within the desired operating temperature range. For instance,the heat exchanger 160 may be configured to provide 550 watts of coolingpower, while the pump source heat exchanger 144 requires 725 watts ofcooling power to maintain the pump source 118 within the desiredoperating range. In one embodiment, the cooling power provided by thecooling circuit 154 is supplemented by the cooling circuit 152 toprovide sufficient cooling power to maintain the pump source 118 withinthe desired operating temperature range.

In one embodiment, the cooling circuit 152 includes a primary heatexchanger 170 that receives a flow of cooled refrigerant through line172, which is used to cool the flow of cooling liquid 158 driven by apump 174 through a fluid pathway 176. At least a portion of the flow ofcooling liquid 158 is driven through the laser element heat exchanger142 by the pump 164 to maintain the laser element 114 within the desiredoperating temperature range.

In one embodiment, the heat exchanger 170 is configured to provide morecooling power than required by the heat exchanger 142 to maintain thelaser element 114 within the desired temperature range. For instance,the heat exchanger 170 may be configured to provide 550 watts of coolingpower, when the laser element heat exchanger only needs 300 watts ofcooling power. In one embodiment, the excess cooling power generated bythe heat exchanger 170 is used to supplement the cooling circuit 154 toensure that the pump source heat exchanger 144 receives sufficientcooling power to maintain the pump source 118 within the desiredtemperature range.

In one embodiment, the additional cooling required by the coolingcircuit 154 is provided by the cooling circuit 152 through the exchangeof cooled liquid through a fluid exchange circuit 180. The fluidexchange circuit 180 includes a delivery line 182 connecting the circuit152 to the reservoir 164, and a return line 184 between the reservoir164 and the circuit 152. A valve 186 controls the flow of a portion 188of the flow of cooling liquid 158 to the reservoir 164 through the line182.

When the temperature of the water flowing through the fluid pathway 166of the circuit 154 is sufficient to provide the cooling needs of thepump source heat exchanger 144, the valve 186 is closed. However, whenthe temperature of the liquid in the pathway 166 is insufficient toprovide the cooling needs of the pump source heat exchanger 144, thevalve 186 is opened to allow a portion 188 of the flow of cooling liquid158 to flow from the fluid pathway 176 of the circuit 152 into thereservoir 164 through the delivery line 182. This flow of cooling liquid188 cools the liquid in the reservoir 164. In one embodiment, a flow ofliquid 189 from the reservoir 164 is delivered back to the circuit 152through the return line 184 responsive to the opening of the valve 186.

This operation cools the liquid in the reservoir 164 and the flow ofcooling liquid 156 driven from the reservoir 164 into the fluid pathway166 by the pump 162. As a result, the flow of cooling liquid 188provides a cooling boost to the flow of cooling liquid 156 that allowsthe pump source heat exchanger 144 to maintain the pump source 118within the desired operating temperature range.

In one embodiment, the opening and closing of the valve 186 iscontrolled using a temperature sensor 190 (e.g., thermocouple) thatmeasures the temperature of the water within the reservoir 164. Thesensor 190 provides an output signal 192 that is indicative of atemperature of the liquid in the reservoir 164. The controller 146(FIG. 1) processes the signal 192 to determine whether the temperatureof the liquid in the reservoir 164 is above or below a thresholdtemperature. If the temperature of the liquid within the reservoir 164has risen above the threshold temperature, the valve 186 is opened toprovide the flow of cooling liquid 188 to the reservoir 164 until thetemperature of the liquid in the reservoir 164 drops below the thresholdtemperature. A corresponding flow of liquid 189 may be returned to thecircuit 152 through the return line 184. When the temperature of theliquid in the reservoir 164 drops below the threshold temperature, thevalve 186 is closed and the cooling circuits 142 and 144 are operated asdescribed above.

It is understood, that the temperature sensor 190 could be replaced by atemperature sensor configured to detect other temperatures in the system100 and provide an output signal indicative of the temperature to thecontroller 146 for use in determining whether the valve should be openedor closed, such as the temperature of the pump source 118, thetemperature of the flow of cooling liquid 156 either upstream ordownstream from the pump source heat exchanger relative to the flow ofcooling liquid 156, or other temperature.

FIG. 3 is a schematic diagram of a chiller 140B in accordance withembodiments of the invention. In some embodiments, the chiller 140Butilizes a single pump 194 to drive flows of cooling liquid through acooling circuit 196 configured to cool the pump source 118, and acooling circuit 198 configured to cool the laser element 114. Thecircuit 196 includes a primary heat exchanger 200, the pump source heatexchanger 144, and a reservoir 202. The pump 194 drives a flow ofcooling liquid 204 from the reservoir 202 along a fluid pathway 206 ofthe circuit 196. The heat exchanger 200 receives a flow of coolingrefrigerant through a cooling line 201, which is used to cool the flowof liquid 204, in accordance with conventional heat exchangers. The flowof cooling liquid 204 is cooled by the heat exchanger 200 and travelsthrough the pump source heat exchanger 144 to cool the pump source 118.The flow of cooling liquid 204 then returns to the reservoir 202.

In some embodiments, the cooling circuit 198 includes a heat exchangeror economizer 210 having an input 212 that receives a flow of coolingliquid 208 from the circuit 196 driven by the pump 194 along a pathway213. The flow 208 travels through the laser element heat exchanger 142to cool the laser element 114 and, optionally, the Q-switch 126. In someembodiments, the flow 208 is returned to the reservoir 202.

In some embodiments, the circuit 198 includes a trim heater 214 and atemperature sensor 216 used to control the temperature of the flow 208through the laser element heat exchanger 142. The temperature sensor 216is configured to output a signal 218 that is indicative of a temperatureof the flow of cooling liquid 208. The controller 146 processes thesignal 218 to determine whether the flow of cooling liquid 208 should bewarmed by the trim heater 214 to ensure that the flow 208 maintains thelaser element 114 within the desired operating temperature range. Forinstance, if the temperature of the flow 208 as indicated by the signal218 drops below a threshold temperature, the controller 146 increasesthe heating of the flow 208 by the trim heater 214. Likewise, thecontroller 146 decreases the heating of the flow 208 by the trim heater214 or deactivates the trim heater 214 when the signal 218 indicatesthat the temperature of the flow 208 is above the threshold temperatureor within a desired temperature range.

It is understood, that the sensor 216 could be replaced by a temperaturesensor configured to detect other temperatures in the system 100 orchiller 140B, and provide an output signal indicative of the temperatureto the controller 146 for use in determining whether the flow of coolingliquid 208 should be heated by the heater 214, such as the temperatureof the laser element 114, the temperature of the laser element heatexchanger 142, the temperature of the flow of cooling liquid 208downstream of the laser element heat exchanger 142 relative to the flow208, or other temperature.

In some embodiments, a portion 220 of the flow 208 discharged from thelaser element heat exchanger 142 is delivered back to an input 222 ofthe heat exchanger 210 along a fluid flow path 224 to temper or preheatthe flow 208 entering input 212 prior to discharging the flow 220through an output 226 of the heat exchanger 210 and returning the flow208 to the reservoir 202 along the fluid pathway 228. This ability topreheat the flow 208 entering the input 212 of the heat exchanger 210may eliminate the need for the trim heater 214.

In some embodiments, the volume of the flow 220 is controlled by a valve230 in a pathway 232, which bypasses the heat exchanger 210. In someembodiments, the valve 230 is controlled in response to a temperature ofthe flow 208 sensed by the temperature sensor 216 or other sensor.

In some embodiments, a temperature sensor 234 is placed in the reservoir202 to sense a temperature of the liquid in the reservoir 202. Thetemperature sensor 234 includes an output signal 236 that is processedby the controller 146 to determine the volume of the flow 220 thatshould be delivered through the heat exchanger 210 along the pathway 224to maintain the temperature of the liquid in the reservoir 202 withinthe desired range. The controller 146 adjusts the valve 230 to a moreopen position to increase a flow 238 through the pathway 232 and reducethe flow 220 through the heat exchanger 210 along pathway 224 when thetemperature of the liquid in the reservoir 202 drops below a thresholdtemperature or temperature range, to warm the liquid in the reservoir202. The controller 146 adjusts the position of the valve 230 to a moreclosed position to reduce the flow 238 through the pathway 232 andincrease the flow 220 through the heat exchanger 210 along the pathway224 when the temperature of the liquid in the reservoir 202 rises abovea threshold temperature or temperature range, to cool the liquid in thereservoir 202.

It is understood, that the sensor 234 could be replaced by a temperaturesensor configured to detect other temperatures in the system 100 orchiller 140B and provide an output signal indicative of the temperatureto the controller 146 for use in determining whether the valve 230should be opened or closed, such as the temperature of the pump source118, the temperature of the flow of cooling liquid 208, or portionthereof, either upstream or downstream from the pump source heatexchanger 142 relative to the flow of cooling liquid 208, or othertemperature.

FIG. 4 is a schematic diagram of a chiller 140C in accordance withembodiments of the invention. In some embodiments, the chiller 140Ccomprises a cooling circuit 240 configured to cool the pump source 118,and a cooling circuit 242 configured to cool the laser element 114. Thecooling circuit 242 comprises a pump 244, a laser element heat exchanger142, and a reservoir 246. The pump 244 drives a flow of cooling liquid248 from the reservoir 246 through a first fluid pathway 250. The laserelement heat exchanger 142 is in the fluid pathway 250 and removes heatfrom the laser element 114 using the flow 248. The flow 248 is thenreturned to the reservoir 246.

The cooling circuit 240 includes a pump 252, a primary heat exchanger254, a pump source heat exchanger 144, and a reservoir 256. The pump 252drives a flow of cooling liquid 258 from the reservoir 256 through afluid pathway 260. The heat exchanger 254 receives a flow of coolingrefrigerant through a cooling line 255, which is used to cool the flowof liquid 258, in accordance with conventional heat exchangers. At leasta portion of the flow 258 travels through the pump source heat exchanger144 where it is used to remove heat from the pump source 118 beforereturning to the reservoir 256. In some embodiments, the temperature ofthe flow of cooling liquid 258 traveling through the pump source heatexchanger 144 is sufficient to provide the desired cooling power to thepump source 118 to maintain the pump source 118 within the desiredoperating temperature range.

In some embodiments, the circuit 242 does not include a primary heatexchanger to cool the flow 248. Rather, a portion 262 of the flow 258 isprovided to the reservoir 256 after it is cooled by the heat exchanger254 to cool the liquid in the reservoir 246 and enable the desiredcooling of the laser element by the flow 248. In some embodiments, aflow of liquid 264 from the reservoir 246 is delivered to the reservoir256 through a fluid pathway 266 to maintain the reservoirs at desiredlevels.

In one embodiment, the chiller 140C includes a three-way valve 270, orequivalent fluid flow control, that receives the flow of liquid 262 in apathway 272. In one embodiment, the valve 270 is configured to directportions of the flow 262 in the pathway 272 to the reservoir 246 througha pathway 274, or to the reservoir 256 through a pathway 276. In oneembodiment, a flow restrictor 278 is placed in line with the pathway 272to control the rate of the flow 262 through the pathway 272 such thatthe desired flow rate of liquid is provided to the heat exchanger 254through the pathway 260.

When the temperature of the flow of liquid 248 traveling through thelaser element heat exchanger 142 is sufficient to provide the desiredcooling of the laser element 114 and, optionally, the Q-switch 126, thevalve 270 is set to deliver the flow of cooling liquid 262 from pathway272 to pathway 276 where it is delivered back to the reservoir 256. Whenthe temperature of the flow of liquid 248 through the laser element heatexchanger 142 is insufficient to provide the desired cooling of thelaser element 114, the valve 270 directs the flow of liquid 262, or aportion thereof, from the pathway 272 to the pathway 274 and into thereservoir 246. This cools the liquid in the reservoir 246 and providesadditional cooling power to the laser element heat exchanger 142 to meetthe cooling demands of the laser element 114. In some embodiments, theflow of liquid 264 is discharged from the reservoir 246 back to thereservoir 256 through the pathway 266 responsive to the delivery of theflow of liquid 262, or a portion thereof, to the reservoir 246.

In one embodiment, the cooling circuit 242 includes a temperature sensor280 having an output signal 282 indicative of a temperature of the flow248, or other temperature relevant to determining whether the laserelement 114 is being maintained within the desired operating temperaturerange. The controller 146 processes the signal 282 to determine whetherthe valve 270 should allow for more or less flow of liquid to thereservoir 246 along the pathway 274. When the signal 282 indicates thatmore cooling power is required for the laser element 114, the controller146 adjusts the valve 270 to allow for a greater portion of the flow 262to travel to the reservoir 246. When the signal 282 indicates that lesscooling power is required for the laser element 114, the controller 146adjusts the valve 270 to reduce the portion of the flow 262 beingdelivered to the reservoir 246. In this manner, the cooling circuit 140Ccan maintain the laser element 114 at a different temperature than thepump source 118.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A laser system comprising: a laser element; apump source configured to input light to the laser element; a firstcooling circuit comprising: a first pump configured to drive a firstflow of cooling liquid through a first fluid pathway; a first primaryheat exchanger in the first fluid pathway configured to cool the firstflow of cooling liquid; and a laser element heat exchanger configured toremove heat from the laser element using the first flow of coolingliquid; and a second cooling circuit comprising: a second pumpconfigured to drive a flow of cooling liquid through a second fluidpathway; a second primary heat exchanger in the second fluid pathwayconfigured to cool the second flow of cooling liquid; and a pump sourceheat exchanger configured to remove heat from the pump source using thefirst and second flows of cooling liquid.
 2. The system of claim 1,further comprising a valve configured to divert a portion of the firstflow of cooling liquid to the second cooling circuit through a feedline.
 3. The system of claim 2, wherein: the second cooling circuitcomprises a reservoir of cooling liquid; and the portion of the firstflow of cooling liquid is received in the reservoir.
 4. The system ofclaim 3, wherein: the system comprises a temperature sensor having anoutput signal indicative of a temperature; and the system comprises acontroller configured to actuate the valve between open and closedpositions responsive to the output signal.
 5. The system of claim 2,further comprising a return line through which cooling liquid isreturned to the first cooling circuit from the reservoir.
 6. The systemof claim 1, wherein: a cooling power delivered from the first and secondcooling circuits to the pump source is configured to maintain the pumpsource within a first temperature range; a cooling power delivered froma second cooling circuit to the laser element is configured to maintainthe laser element within a second temperature range; and the first andsecond temperature ranges are different.
 7. The system of claim 6,wherein the first temperature range is approximately 21-34° C.
 8. Alaser system comprising: a laser element; a pump source configured toinput light to the laser element; a first heat exchanger configured tocool a first flow of cooling liquid; a pump source heat exchangerconfigured to remove heat from the pump source using the first flow ofcooling liquid; a laser element heat exchanger configured to remove heatfrom the laser element using a second flow of cooling liquid; and a pumpconfigured to drive the first and second flows of cooling liquid.
 9. Thesystem of claim 8, further comprising a second heat exchangercomprising: a first input configured to receive the second flow ofcooling liquid; and a first output discharges the second flow of coolingliquid received at the first input to the laser element heat exchanger.10. The system of claim 9, wherein the second heat exchanger comprises:a second input configured to receive at least a portion of the secondflow of cooling liquid, the second input located downstream of the laserelement heat exchanger relative to the second flow of cooling liquid;and a second output discharges the portion of the second flow of coolingliquid received at the second input.
 11. The system of claim 10, furthercomprising a reservoir fluidically coupled to the second output andconfigured to receive the first and second flows of cooling liquid. 12.The system of claim 11, further comprising: a fluid pathway fluidicallyconnecting the laser element heat exchanger and the reservoir andbypassing the second heat exchanger; a valve in the fluid pathway; atemperature sensor having an output signal; and a controller configuredto actuate the valve between open and closed positions based on theoutput signal to control a portion of the second flow of cooling liquidtraveling through the fluid pathway.
 13. The system of claim 8, furthercomprising: a temperature sensor having an output signal indicative of atemperature; a heater configured to heat the second flow of coolingliquid upstream of the laser element heat exchanger relative to thesecond flow of cooling liquid; and a controller configured to controlthe heater based on the output signal.
 14. The system of claim 8,wherein: the pump source heat exchanger is configured to maintain thepump source at a first temperature using the first flow of coolingliquid; the laser element heat exchanger is configured to maintain thelaser element at a second temperature using the second flow of coolingliquid; and the first and second temperatures are different.
 15. A lasersystem comprising: a laser element; a pump source configured to inputlight to the laser element; a first cooling circuit comprising: a firstpump configured to drive a first flow of cooling liquid through a firstfluid pathway; a laser element heat exchanger in the first fluid pathwayconfigured to remove heat from the laser element using the first flow ofcooling liquid; and a first reservoir from which the first flow ofcooling liquid is discharged; and a second cooling circuit comprising: asecond pump configured to drive a second flow of cooling liquid; aprimary heat exchanger configured to cool the second flow of coolingliquid; a pump source heat exchanger configured to remove heat from thepump source using at least a portion of the second flow of coolingliquid; and a second reservoir configured to receive the portion of thesecond flow of cooling liquid fed to the pump heat exchanger; whereinthe first reservoir is configured to receive a portion of the secondflow of cooling liquid output from the primary heat exchanger.
 16. Thesystem of claim 15, wherein the second reservoir is configured toreceive a flow of liquid from the first reservoir.
 17. The system ofclaim 16, further comprising a valve configured to receive the portionof the second flow of cooling liquid and direct the portion of thesecond flow of cooling liquid to the first and second reservoirs. 18.The system of claim 17, further comprising: a temperature sensor havinga sensor output signal indicative of a temperature of the first flow ofcooling liquid; and a controller configured to adjust the portion of thesecond flow of cooling liquid discharged from the valve to the first andsecond reservoirs based on the sensor output signal.
 19. The system ofclaim 18, further comprising a flow restrictor placed in line with afluid flow path delivering the portion of the second flow of coolingliquid to the valve, the flow restrictor controls a flow rate of theportion of the second flow of cooling liquid in the fluid flow path. 20.The system of claim 15, wherein: the first cooling circuit is configuredto maintain the laser element at a first temperature using the firstflow of cooling liquid; the second cooling circuit is configured tomaintain the pump source at a second temperature using the second flowof cooling liquid; and the first and second temperatures are different.